Re: [Xen-devel] Upstream QEMU based stubdom and rump kernel

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 17 Mar 2015, Anthony PERARD wrote:
> On Tue, Mar 17, 2015 at 02:29:07PM +0000, Wei Liu wrote:
> > I've now successfully built QEMU upstream with rump kernel. However to
> > make it fully functional as a stubdom, there are some missing pieces to
> > be added in.
> > 
> > 1. The ability to access QMP socket (a unix socket) from Dom0. That
> >    will be used to issue command to QEMU.
> 
> The QMP "socket" does not needs to be a unix socket. It can be any of
> those (from qemu --help):
> Character device options:
> -chardev null,id=id[,mux=on|off]
> -chardev 
> socket,id=id[,host=host],port=port[,to=to][,ipv4][,ipv6][,nodelay][,reconnect=seconds]
>          [,server][,nowait][,telnet][,reconnect=seconds][,mux=on|off] (tcp)
> -chardev 
> socket,id=id,path=path[,server][,nowait][,telnet][,reconnect=seconds][,mux=on|off]
>  (unix)
> -chardev udp,id=id[,host=host],port=port[,localaddr=localaddr]
>          [,localport=localport][,ipv4][,ipv6][,mux=on|off]
> -chardev msmouse,id=id[,mux=on|off]
> -chardev vc,id=id[[,width=width][,height=height]][[,cols=cols][,rows=rows]]
>          [,mux=on|off]
> -chardev ringbuf,id=id[,size=size]
> -chardev file,id=id,path=path[,mux=on|off]
> -chardev pipe,id=id,path=path[,mux=on|off]
> -chardev pty,id=id[,mux=on|off]
> -chardev stdio,id=id[,mux=on|off][,signal=on|off]
> -chardev serial,id=id,path=path[,mux=on|off]
> -chardev tty,id=id,path=path[,mux=on|off]
> -chardev parallel,id=id,path=path[,mux=on|off]
> -chardev parport,id=id,path=path[,mux=on|off]
> -chardev spicevmc,id=id,name=name[,debug=debug]
> -chardev spiceport,id=id,name=name[,debug=debug]
> 
> > 2. The ability to access files in Dom0. That will be used to write to /
> >    read from QEMU state file.
> 
> To save a QEMU state (write), we do use a filename. But I guest we could
> expand the QMP command (xen-save-devices-state) to use something else, if
> it's easier.
> 
> To restore, we provide a file descriptor from libxl to QEMU, with the fd on
> the file that contain the state we want to restore. But there are a few
> other way to load a state (from qemu.git/docs/migration.txt):
> - tcp migration: do the migration using tcp sockets
> - unix migration: do the migration using unix sockets
> - exec migration: do the migration using the stdin/stdout through a process.
> - fd migration: do the migration using an file descriptor that is
>   passed to QEMU.  QEMU doesn't care how this file descriptor is opened.

QEMU would definitely be happy if we started using fds instead of files
to save/restore the state on Xen.

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